Hemophagocytic lymphohistiocytosis (HLH) is an aggressive, life-threatening syndrome of excessive immune activation. Presentation is most common among the pediatric population, and cases in adults are rare. The number of nonhematologic presentations described in relation to HLH has been growing. We present a case involving a woman who developed HLH after autologous stem cell transplantation for mantle cell lymphoma. Months later, she received a diagnosis of pulmonary arterial hypertension (PAH) while undergoing treatment for her HLH. To our knowledge, PAH associated with adult HLH has only been described in the literature once before. PAH may now be a potential differential diagnosis for patients with HLH who present with respiratory symptoms.